Electric switch



May 14, 1940.

c. A. scHAEFf-:R

ELECTRIC swITcH Filed' May 4, 195e 4 Sheets-Sheet l n/w ATTORNEY c. A. scHAEr-'l-:R 2,200,970

ELECTRIC SWITCH May 14, 1940.

Filed May 4, 1936 4 Sheets-Sheet 2 INVENTOR *E E KfZ/7. Scdefe."

ATTORNEY May i4 1940 c. A. SCHAEFER 2,200,970

ELECTRIC SWITCH INVENTOR Cdrl Scaefer ATTORNEY y 14, 1940. C, Af SCHAEFERy 200,970 ELECTRIC SWITCH Filed May 4, V1050 4 sheets-sheet 4 si N D" Il F 'l @e 'l :i5 XI [gl/.' :XI H l H @E i a m05. BY f// ATTORNEY PATENT OFFICE ELEc'rmo swrron carl A. Schaefer, Detroit, Mien., assigner to Square D Company, Detroit, Mich., a, corporation of Michigan Application May 4, 1936, Serial No.I 77,723

27 claims.

This invention relates to devices for making and breaking electrical circuits and more particularly to electric switches automatically operable in response to variations in an exterior condition such as pressure', temperature, liquid level, etc.

One object of the invention is to provide an improved contact operating mechanism for an electric switch providing a quick make and break operation.

Another object of the invention is to provide improved means for Calibrating an automatic electric switch including a Calibrating spring acting on the pressure responsive element and which may be provided as part of a bellows assembly.

Another object of the invention is to provide means for establishing a relatively permanent limiting setting for the diierential at which the switch operates.

Another object of the invention is to provide an improved form oi differential adjustment for an automatic electric switch.

Another object of the invention is to provide an overload relay for an automatic electric switch which operates directly upon the contact actuating mechanism of the switch and which may be readily detached as a unit from the switch without disturbing its normal operating mechanism.

Another object of the invention is to provide an improved form of current responsive overload for an electric switch.

Another object of the invention is to provide an improvedunit assembly of current responsive overload relay, manual operating means and relay resetting means for an automatic electric switch.

Another object of the invention is to provide an electric switch including pressure responsive means for normally actuating the switch, auxiliary pressure responsive means for actuating switch and manual and/or current responsive means for actuating a switch.

Another object of the invention is to provide means for sealing a slot inthe switch housing which receives means for indicating the range adjustment of the switch.

Other objects and features will be readily apparent to those skilled in the art from the following specification and the appended drawings illustrating certain preferred embodiments of the invention in which:

Figure l is a front elevational View of one form of an electric switch according to the present invention.

Figure 2 is an enlarged view similar to Figure 1 with the front cover'plate removed and parts broken away to shown internal parts.

Figure 3 is a vertical sectional view taken `on the line liII-III of Figure 2. y I

Figure 4 is a vertical sectional view taken on the line IV-IV oi Figure 2. Figure 5 is a horizontal sectional view taken on the line V--V of Figure 2.

Figure 6 is a partial sectional view taken on the line VI-VI of Figure 4.

Figure 7 is a partial view similar to Figure 2 with thecontacts separated by the high pressure operated mechanism.

Figure 8 is a partial view similar to Figure 2 with the contacts separated by the normal pressure operated mechanism.

Figure 9 is a front elevational view of a different form oi front cover where the switch includes thermal overload and manual operating means.

Figure 10 is a partial front elevational view similar to Figure 9 with the cover removed.

Figure l1 is a horizontal sectional View taken on the line XI-XI of Figure 9.

Figure 12 is a partial view similar to Figure 10 but showing the contacts separated manually.

Figure 13 is a detail sectional view taken on the line XIII- XIII of Figure l0.

Figure 14. is a top plan view of a modified form of adjusting means.

Figure 15 is a vertical sectional view of the switch shown in Figure 14.

. Figure 16 is a fragmentary detail view showing the connection of the device for normal actua-A tion in the reverse direction than that shown in the previous figures.

The switch illustrated in Figures 1 to 8, inclusive, comprises a housing I including a removable front cover 2. The housing is provided with various openings for the reception of conduit connector 3, normal pressure responsive actuating means 4 and means responsive to predetervmined maximum pressure setting 5. The interior of the housing includes a projecting portion 6 against which is secured a U-shaped magnetic piece 'I by means of a conducting plate 8 insulated from the magnet by a sheet of iibre or other. material 9. The plate 8 may be releasably held in position by a stud II which may thread into the plate. A bent up portion I2 may be provided at the iront edge of the plate 8 to provide a terminal connector. A bent up portion I3 is provided at a back edge of the plate 8 for connection to the leaf spring I4 as by means of the stud I5. The leaf spring I4 carries a stationary contact I6 and is adjustably maintained in position by bearing against the cam surface ll. This cam surface is preferably formed of insulating material and may be integral with an accessible portion I8 having an opposite reduced end portion i9 projecting through an opening in the plate 8 to provide a bearing. The accessible portion I3 may be provided with a slot for the reception of a screwdriver or other means for rotation of the cam surface Il. The cam surface is provided with a projecting portion 2| and the housing carries an adjusting screw 22 as a means for a relatively permanent setting preferably at the factory for the minimum differential to which the ordinary adjusting means can set the switch. The enlargement 2| strikes the screw 22 in its clockwise movement, as seen in Figure 5 to limit the movement of the stationary contact i3 toward the right and hence the minimum differential for the switch as will be more fully explained hereinafter.

To the bottom of the housing is rigidly secured a U-shaped supporting bracket 23 by means of studs 24. The opposite upstanding legs of the bracket are each equipped with a pair of spaced threaded openings, 25, 26. Studs 21 having shaftlike bearing portions at their ends are threaded into the opposite holes 25 and project into bearing openings 28 in a pair of separately movable switch arms 29 and 3|. These switch arms may carry openings 32 for cooperation with the openings 26 in the supporting bracket in a manner to be hereinafter described. These arms have generally nat substantial vertical portions equipped adjacent the bottom with overlapping iianges 33 and 34 in which the bearing openings 28 and 32 are located.

The arm 3| is formed of conducting material such as aluminumv or brass and carries adjacent its upper end a movable contact 35. A reduced connecting portion between the contact 35 and the arm 3| is loosely received within a slot 36 at the top of arm 29 and provides for limited relative movement between the arms. The arm 29 is formed of steel or other magnetic material and is disposed closely adjacent the opposite poles of the magnet l in the closed position of the contacts as shown. A small tension spring 31 connected at one end to a stationary part on the bracket 23 and its other end to the arm 3| biases this arm toward the contacts engaged position. A pin 38 connects the opposite flanges on the arm 29 and is adapted to be engaged by an insulating part 39 on a pivoted lever 4|. A flexible lead 42 connects the arm 3| to the back leg of the bracket 23 and the front leg of the bracket may be provided with a terminal portion 43 for the reception of a circuit conductor. A support 44 integral with the housing projects from the back wall thereof and provides a means for connection of the cover plate. A Wall 45 connects projection 44 to the top interior wall of the housing and a stop 46 is provided on this wall to limit the contact separated position of the switching arm.

Thenormal pressure responsive element 4 includes an exterior casing 41 having a connection means 48 secured thereto providing access to the interior of the housing 41. Within the housing 4l is disposed a corrugated bellows portion l49 having a bottom plate 5| brazed or otherwise secured thereto. The bellows portion 49 is rigidly secured at its upper end to an annular portion 52 which is in turn secured to the interior of the housing 41. An actuating pin 53 is secured to the bellows plate 5| and extends upwardly into the switch housing. A washer 54 loosely surrounds the pin 53 and is disposed on top of the annular portion 52. An adjusting nut 55 is threaded on thc upper end of pin 53 and a calibrating spring 56 is disposed between the washer 54 and the nut 55 and tends to bias the pin 53 upwardly. The end of the pin is provided with a bearing point 51 received within a corresponding impression in the lever 4|. This lever is U-shaped in cross section as shown in Figure 3 and is pivoted to projections 58 on the interior of the housing by means of a shaft 59.

Upon the upper side of the lever 4| is disposed a compression spring 6| having its upper end received in a slightly cup-shaped member S2 which is rigidly connected to a sleeve 33 threaded on an adjusting screw 64 having its end accessible at 'the top oi the casing and there provided with' a screwdriver slot for rotation. The front and back of the cup-shaped member 62 are extended as at 65 and 6B. The yback extension 65 is prevented from rotating by a pair of spaced projections 61 on the back interior wall of the housing and this projection 65 is guided by the projections 5i' for longitudinal movement in the adjustment of the range of operation of the device. To the front extension 66 is rigidly secured a leaf spring 58 carrying an indicating pin S9 at a generally mid point. The front cover for the switch is provided with a. slot having indicia therealong and the pin 69 is adapted to indicate the adjustl ment of the device by its position adjacent these indicia. When the front cover is in place the spring 68 presses against `the slot and serves to seal the opening of the cover. The length of the spring 68 is roughly twice that of the slot so thatwhen the -pin is placed at a mid point the spring substantially closes the slot in both extreme positions of the pin corresponding to the extreme limits of adjustment. As the screw S4'is turned from the exterior of the housing, the threaded sleeve S3 and the generally cup-shaped member 52 attached thereto will move downwardly and compress spring 6|, thus changing the pressure exerted thereby upon the lever 4|. A collar l2 on the end of the screw 54 is engaged by the sleeve "63 to limit the. extreme compression of the spring 6|. The screw 64 is provided with an upper collar 13 and a plate 'I4 is disposed against the inside top of the housing to provide a bearing surface for this collar.

The insulating member 39 constitutes an extension on the lever 4|, being rigidly secured thereto as by riveting. The upper surface of this member is provided with a projection 'l5 adapted to contact with a downward projection 'l5 on the central support 44 to limit the upward movement of the lever 4|. An extension 11 is provided on the inside bottom of the housing to limit the lower movement of the lever.

The portion of the switch which has now been described constitutes the normal operating switching mechanism by which the movable contact automatically moves to engaged and sepa rated position in response to a change in pressure within the bellows chamber. This much of thel device constitutes a complete switch in itself and the other apparatus shown in the drawings and to be later described constitutes an auxiliary device for operating the switch in response to a diifercnt condition. The operation of that portion of the 5 lil) lll

tion. The operation of the switch is dependent upon the resultants of the force exerted on the lever arm il by the range spring 6l and that exerted on this lever by the bellows pin 53. With the parts shown in Figures 2, 4 and 6, the pressure within the bellows chamber aided by the Calibrating spring 56 is sufficient to overcome the force exerted on the lever arm by the range spring 9i. lf this pressure decreases the range spring will move the lever 6l downwardly whereupon the insulating end portion 39 on the lever engages the pin 38 on the arm 29 and pulls it downwardly. When the moment of this force about the pivot ol the arm is sufficient to overcome the moment of the attraction of magnet 'l on the arm 29, this arm will move in a clockwise direction. The rst part of this movement does not separate the contacts as the construction provides for a limited relative movement between the levers 29 and 3l. As the arm 89 moves away from the magnet the force exerted thereby rapidly decreases so that by the time the arm 29 engages the arm 3l it will move the movable contact 95 to the disengaged position with a snap action. These arms will then move together in a clockwise direction until they engage the stop t@ as shown in Figure 8. When in Figure 8, as the pressure within the bellows increases, the force exerted by the pin 53 from the bellows and the Calibrating spring 55 will overcome the force exerted by the spring 6l and the lever lll will be moved upwardly, thus permitting arms 3l and 29 to move toward contacts engaged position under the bias of the spring 3l. Before the contact 35 engages the stationary contact I6 the magnetic arm 29 will have approached within a substantial portion of the field of the magnet 'l whereupon the arm 29 will quickly pull the contact 35 into its engaged position so that the engagement of the contacts will also occur with a snap action. It is to be noted that in the on position the magnetic arm 29 bears against the stationary contact 35 so that the contact pressure is supplied not only by the spring 31 but also by the force exerted by the magnet on the arm 29. To adjust the range at which the switch operates the screw 64 is turned from the exterior of the casing, thus increasing or lessening the compression on spring Bl and thereby increasing or lessening the pressurenecessary to be exerted by the bellows element to cause motion of the lever 4l. The calibrating spring 56 may be varied by removing the front cover and turning the knurled nut 55. This Calibrating spring exerts a pressure on the bellows pin in the same direction as an increase in pressure by the bellows and serves to provide an adjustment which .may be used for factory calibration of the range. Thus, if the total range of the spring 8l is 50#, adjustment of vthe calibrating spring 56 will determine the point at which the 50# range occurs. This Calibrating spring further serves to provide for operation at a vacuum as when this spring is adjusted for tension greater than the range spring 6l the resultant force on the lever lll is upward thus requiring a vacuum or suction to move the lever 4l downwardly.

The differential adjustment provides means for varying the limits between the engagement and disengagement of the contact. This is done by turning the element I8 whereupon the cam surface l1 varies the position of the stationary contact and by this varies the distance between the magnetic arm 29 and the magnet 1 in the contacts engaged position. When the stationary contact lli is at its farthest position to the right as viewed in Figure 5, the magnetic gap will be greatest and the differential at a minimum. When the stationary contact is at its farthest position to the left, as viewed in Figure 5, the magnetic gap will be least and the differential at a maximum. The parts are assembled to have a given maximum setting of differential and the minimum setting is adjusted by the screw 22. lt is obvious that the minimum setting could be determined by assembly and the maximum set` ting adjusted by the screw 22 in the same manner.

ln the switch illustrated in Figures l to 9, inclusive, there is included means for positively moving the contact 35 to its disengaged position irrespective of the pressure on the bellows eleu ment il. This device constitutes what is known as a high pressure cutout and includes a pressure responsive unit denoted generally at 5 having a bellows 'lll carrying a pin liti. spring 99 is disposedaround the pin and bears against the bellows to oppose its movement. An adjusting screw 99 of cylindrical form is threaded into a fixed part and bears against the upper end of the spring lill. The pin lll slidably projects through the screw 99 into a housing i9 carrying a supporting bracket ill 'having a slot in its front face. A plate-like element 88 constituting one arm of an over center toggle has a pair of projections extending into the slot in the front face of bracket 8l and its opposite edge is provided with a point connection 83 with a spring holding member 84. An opposite spring holding member 85 has a point connection 86 with an adjusting screw 8l. A compression spring 88 is disposed between the members 84 and 85. This spring simply constitutes theother arm of the over center toggle. A pin 89 extends upwardly into the switch housing and is biased against the plate 82 by a compression spring 9|. A shaft 92 is provided between thc opposite sides of the supporting .bracket 23 and upon this shaft is pivotally mounted a lever 93 biased by a spring 94 in a counterclockwise direction. The lever 93 is provided With an arm 95 in the path of the pin 89.

The high pressure cutout is adapted to be connected to a controlling device such as a high pressure side of a refrigerator system and when the pressure reaches a predetermined maximum the force of the bellows pin 18 will snap the toggle formed by the arm 82 and the spring 88 into its over center position, thus snapping the pin 89 quickly in an upward direction. The upper end of the pin 89 then engages the arm 95 on the lever 93 and moves into position shown in Figure 7, wherein the end of the lever has engaged arm 29 and thus positively moved the contact 35 to the disengaged position. If the pressure within the bellows 5 thereafter decreases until it is no longer suflicient to hold the toggle in its over center position the toggle will snap over and the pin 89 will permit the lever 93 to move to its original position under the bias of spring'94. When this happens the contact will again be under the control of the normal operating mechanism.

It is to be noted that in thus opening the contacts the high pressure cutout does not in any case have to be operated against the pressure exerted by the bellows 4 or the spring 6I as it is seen that the movement ol the contact arms from engaged position tends to move the pin 38 away from the insulating portion 39 of the lever 4l and hence there is no counteracting of thc action of the high pressurec'utout by the normal A compression operating mechanism. This is clearly seen by thereof.

an inspection of Figure 7 where if the bellows 4 is exerting a high pressure the lever 4i will be up and the contacts engaged and the lever 93 when operating to disengage the contacts wili simply move the pin 3d away from the portion 30 oi the lever iti. If on the other hand the lever 4| should be in a downward direction the contacts will already have opened and if the high pressure cutout is somehow operated the lever 93 will simply move until it engages the contact assembly in disengaged position. Adjustment of the range of the high pressure cutout is determined by `the adjusting screw d0 which` varies the force on the bellows lli. Adjustment of the differential of operation. of the high pressure cutout is determined by the adjusting screw 8l which varies the tension exerted by the spring 88 and hence the force necessary to move it over center. A. locking nut 0B may be provided on the screw 8l to prevent accidental adjustment For mounting the switch in place a metallic bracket 3T is mounted on the exterior back wall of the housing and projects beyond the ends thereof where it is provided with holes 98 for the reception of mounting screws. The support 4t is provided with a metallic insert into which the cover screw 30 may be threaded to secure the front cover into position.

For the sake of simplicity in the drawings, the switch according to the present invention having thermal overload relay and manual opn eration has been shown separately in Figures 9 to 13, inclusive, and the normal operating mech anism and high pressure cutout have been only partially shown. The=thermal overload relay and the manual operating mechanism are mounted together on a unitary insulating base |0I and include a current responsive element of the solder pot type embodying a ratchet wheel |02 mounted on a shaft and normally held against rotation by a solidified metal Within the cylindrical container |03. A resistor coil Hifi surrounds the container |03 and is serially connected in the circuit through the switch by terminal screws |05 and |06. The terminal screw |06 is threaded into a conducting plate |01 carrying a terminal screw- |08 for the reception oi a circuit conductor. Terminal screw is threaded into the terminal I2 previously de scribed. To improve the electrical connection between the end of resistor coil |04 and terminal i2 a U-shaped piece of copper or other conducting material |03 may be disposed about the corner of the base |0| so that one side of the conducting piece bears against the terminal I2 and the other side against the end of the resistor coil, the conducting parts being held in place solely by the screw |05.

The base is provided with a slot in which is disposed a generally rectilinearly movable element H2 carrying a striker H3 on one end adapted to engage a projection H4 on the magnetic arm 23 in moving to the right as shown in Figure 13. Member ||2 is provided with an indicating extension ||5 having a part disposed closely adjacent to the corresponding front portion of Ithe switch housing cover and carrying indicating means disposed adjacent an opening ||6 in the cover to show the tripped or set condition of the relay. The member |2 is furthermore equipped with a latching projection Hl? adapted to engage with the teeth on the ratchet wheel |02 to hold the element I2 in its lefthand position as viewed in Figure 13. The member l2 is guided at its lefthand end within an opening H8 in the base |0| and at its righthand end by a pin H0 spanning the slot I|| in the base |04. A spring |29 interconnects a stationary post on the base with the extension H5 and biases the member ||2 for movement toward the right and also for rotation about the pin H9 as it is located considerably above the plane oi the pin. This insures the latching of the projedtion ill with the teeth of the ratchet and the movement of the member toward the right when released. With passage of an overload current through the switch the heat generated by the coil |04 will be sufficient to fuse the binding metal within the cylinder |03 whereupon the shaft holding the ratchet wheel |02 will be free to rotate and the member ||2 will be released for movement toward the right under the action of its biasing spring. This movement causes the striker ||3 to engage the extension |54 on the arm 2@ and moves the contact 35 to separated position. It is to be noted that this move-u ment, similar to that caused by the high pressure cutout, is free from any resistance from the normal operating mechanism.

For manually moving the contacts to disengaged position and for resetting the thermal operation,` a rotary shaft |22 pivotally extends through the base i0| and at the back of this base has an insulating striker arm |23 rigidly connected thereto. This striker arm is adapted to engage a projection 524 on the arm 20 and move the contact 35 to separated position as shown in Figure l2.

At the iront of the base |0| an arm i2@ is also rigidly secured to the shaft |22 and is adapted when. rotated to Contact with the member il2. A spring guide |26 is pivotaliy atached to a part connected to the arm |25 and a spring lil is disposed thereon between the end of the guide and a stationary bracket |28 and is adapted to be moved over center by rotation of the handle to secure accelerated movement for the manual operation. An elongated stud 929 is threaded into the support 44 to rigidly support the base in position. The cover screw 99 is then ,threaded into the head of the stud |29 to hold the cover in position. Where the manual and overload are used the cover is provided with a. bo7r-like portion |3| to provide clearance for the base |0| and the mechanism mounted thereon. A manual operating handle |32 is pivotally mounted on the cover and has a portion projecting therethrough ending in a tongue |33 received within v a slot |34 in the shaft |22.

The operation of both the thermal overload and the manual operator should be readily apparent. The circuit for the switch passes from the terminal |08 through the plate |01, through the resistor coil |04, through the terminal 05 and conducting strip |09 to the extension l. on the plate 8 from which'it passes through the extension I3 and the leaf spring |4 to the station ary contact I6, thence from the movable contact 35 through the arm 3| and the flexible lead 42 to the bracket 23 and the opposite circuit terminal 43. When the current through the switch is be yond the rating of the current responsive part of the thermal overload relays the heating from the coil |04 will fusie the metal within the container |03,and release the ratchet wheel |02, whereupon the member I I 2 will move to the right and the striker I3 engagingthe extension H13 on the lever 29 will cause themovable contact 35 to move to its separated position. To reset the thermal overload the manual operating memaecomo ber |32 is rotated clockwise, whereupon the arm |25 engages the member |2 and moves it to the left and into relatching engagement with ratchet wheel ||l2. If the metal in cylinder |03 has solidied the ratchet is held against rotation and member ||2 will be latched in its reset position with the striker out of engagement with the extension H4. To manually open the contacts the manually operated member is rotated clockwise,

whereupon striker |23 engages extension E24 and moves the movable contact 35 to the disengaged position. Rotation of the manually operated member |32 thereafter in a counterclockwise direction will move the striker |23 out of the path of the extension H24 and return the control of the movable contact to the normal operating mechanism. The position of the parts as shown in Figure 12 correspondsto manual oir position and also to reset position for the overload relays,

In the normal movement of the manual operator to on and off position, the movement is accelerated by the movement of the spring |21 over its dead center position. It is noted that in the resetting of the member H2 the arm |23 i engages the extension |24 and prevents the contacts from returning to engaged position While the overload is disabled by being reset. After reset, the manually operated member is turned counterclockwise to place the control again in the normal operating mechanism. It is noted that the movement of the contacts to disengaged position by the thermal overload relay, by manual operation and by the high pressure cutout are all three accomplished without resistance from the normal operating mechanism and that while each of these three elements positively moves the movable contact to disengaged position, none of them positively moves it to engaged position but simply restores the control of the contact to the normal operating mechanism and permits this mechanism to move the contact to engaged position if its operating characteristics are so set. It is to be noted that While the manual operator and thermal overload relay both actuate the movable contact to disengaged position, these elementscan be attached and detached as a unit without changing the normal operating mechanism. All that is necessary is to remove the stud H29 and screw |05 whereupon the base and the entire manual and overload relay may be disassembled from the switch without disturbing the normal operating mechanism. This is a highly desirable feature as it provides obvious economies in substituting one relay unit for another and also provides for the ready attachment of a relay unit to an existing switch in the field. Due to the connection of the tongue. |33 with slot |34 in the shaft |22 the cover may be readily removed `from the switch without disturbing the unit assembly made up by the overload relay and manual operating mechanism other than to remove the exterior manual 'operating handle.

Figures 14 and 15 show a modified arrangement for securing adjustment of the differential and the range by means of exterior knobs rather than by the screwdriver adjustment heretofore described. In this connection, the screw 64 for adjusting the range is extended through the cover and a knob |35 is attached thereto by a set screw |36. In the diierential adjustment the element I8 is extended beyond the cover and a knob |31 and an indicating scale |38 attached thereto by a set screw |39. In this construction the indicating scale |38 has a tongue |4| bent therefrom and disposed against a flat portion on the member I8 whereupon the single set screw |39 serves to securely hold the knob and indicating scale on the shaft extension.

Figure 16 shows the arrangement of the parts for what is vknown as direct action. Here the trunnion studs 21 have been threaded into the openings 26 in the supporting bracket 23 and project into the openings 32 in the arms 29 and 3| pivoting them at this point. The insulating end portion 39 on the lever 4| is 1n the reverse direction and engages with the pin 38 when moved upwardly. The pin 38 is now at the left of the pivot point of the switching arms so that movement of this pin upwardly oy an increase in pressure in the bellows moves the contact to separated position. It is to be noted that in this changing 'from reverse to direct action the length of the lever arm 4| to the pin 38 remains the same and the distance between the pin 38 and the pivot point of the switching arms remains the same so that the operating forces will be comparable as the moment arms through which they are applied are substantially the same. n

While certain preferred embodiments of the invention have been specifically disclosed, it is understood that the invention is not limited thereto as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims.

What is claimed is: l

l. In an electric switch, a pair of generally parallel, rigid arms, each pivotally mounted on a relatively xed part and each having limited relative movement independently of the other about l its pivotal mounting on said part, a Contact element supported on one of said arms, an opening in the other' of said arms through which said contact element loosely extends, a stationary contact cooperating with said contact element to complete a circuit through the switch, and means for moving said other arm into engagement with said one arm to move said contact element to separated position.

2. In an electric switch, a pair of generally parallel, rigid arms, each pivotally mounted on a relatively xed part and each having limited relative movement independently of the other about its pivotal mounting on said part, a contact element supported on one of said arms, a stationary contact cooperating with said contact element to complete a circuit through the switch, means biasing said one arm toward contactsengaged position, a magnet element holding the other of said arms in ksaid position, and means for moving said other arm against the force of said magnet to engage said one arm with a snap action and move it to contacts-separated position.

3. In an electric switch, a pair of generally parallel, rigid arms, each pivotally mounted on a relatively fixed part and each having limited relative movement independently of the other about its pivotal mounting on said part, a contact element supported on one of said arms, a stationary Contact cooperating with said contact element to complete a circuit through the switch, means biasing said one arm toward contactsengaged position, a magnet element attracting the other of said arms into said position, means limiting the movement of said other arm toward said magnet, and means for moving said other arm away from said magnet to move the contact element to separated position.

4. In an electric switch, a pair of generally parallel, rigid arms, each pivotally mounted on a relatively fixed part and each having limited relative movement independently of the other about its pivotal mounting on said part, a contact element supported on one of said arms, a stationary contact cooperating with said contact element to complete a circuit through the switch, means biasing said one arm toward contactsengaged position, a magnet element. attracting the other of said arms into said position, means limiting the movement of said other arm toward said magnet, and means for moving said other arm away from said magnet to move the contact element to separated position, said limiting means being adjustable to vary the differential at which the switch operates.

5. In. an electric switch, a pair of generally parallel, rigid arms, each pivotally mounted on a relatively xed part and each having limited relative movement independently oi' the other about its pivotal mounting on said part, a contact element supported on one of said arms, an opening in the other of said arms through which said contact element loosely extends, a stationary contact cooperating with said contact element to complete a circuit through the switch, means biasing said one arm toward contacts engaged position, a magnet elementv attracting said other arm into said position, and means on said contact element engageable by said other arm in said position to limits its position with respect to said magnet and to increase contact pressure, and means for moving said other arm away from said magnet to move the contact element to separated position.

6. In an electric switch, a rigid switching arm pivotally mounted on a fixed part, a contact surface on said arm, a stationary contact cooperating with said contact surface to 4complete a circuit through the switch, a magnetic element movable in the path of said arm independently thereof, spring means biasing said switching arm toward contacts engaged position, a magnet biasing said magnetic element out of engagement with said arm to permit the contact and contact surface to be engaged under the action of said spring biasing means, and pressure responsive means for moving said magnetic element away from said magnet to move the switching arm to contacts separated position.

'7. In an electric switch, a rigid switching arm pivotally mounted on a lixed part, a contact surface on said arm, a stationary contact cooperating with said contact surface to complete a circuit through the switch, a magnetic element movable in the path of said arm independently thereof, a magnet biasing said element out of engagement with said arm, and operating mechanism automatically responsive to exterior .conditions for moving said element away from the magnet to movethe arm to contacts separated position and for moving said element and arm into their contacts engaged position,

8. In an electric switch, a rigid contact member pivotally mounted on a fixed part and movable to oif and on positions, a magnetic element movable independently of said member and having a limited lost motion with respect thereto, spring means biasing said member toward on position, a magnet biasing said element to a position corresponding tothe on position of said member, and mechanism automatically responsive to an exterior condition for moving said element away from said magnet to move the member to oif position.

9. In an electric switch, relatively movable contacts, means responsive to an exterior condition for moving said contacts to separated and engaged positions, a rotary cam for varying the differential in said condition between said opposite movements, an abutment connected with said cam, and an adjustable stop adapted to cooperate with said abutment to provide a relatively permanent setting of the extreme position to which said cam may be moved.

10. In an electric switch, stationary and movable contacts, a magnetic arm movable to move said movable contact to disengaged position, means responsive to an exterior condition for moving said arm, a magnet biasing said arm against movement to contacts disengaged position, and means for varying the space between said arm and said magnet in the contacts engaged position to provide a differential adjustment, and means for adjustably limiting the maximum space obtainable by said space varying means.

11. In an electric switch, stationary and movable contacts, a magnetic arm movable to move said movable contact to disengaged position, mechanism responsive to an exterior condition for moving said arm, a magnet exerting a force tending to hold said arm in contacts engaged position, the position of said arm with respect to said magnet being limited by the engagement of said contacts, a resilient mounting for said stationary contact, a cam surface for positively backing said stationary contact, and means for moving said cam surface to vary the position of said stationary contact and the space between said arm and magnet in the contacts engaged position.

12. In an electric switch, stationary and movable contacts, a magnetic arm movable to move said movable contact to disengaged position, mechanism responsive to an 'exterior condition for moving said arm, a magnet exerting a force tending to hold said arm in contacts engaged position, the position of said arm with respect to said magnet being limited by the engagement of said contacts, a movable cam surface, a spring arm movable by said cam surface, the stationary contact being mounted on said arm, whereby the space between said arm and magnet in the contacts engaged position may be varied.

13. In an electric switch, stationary and movable contacts, a magnetic arm movable to move said movable contact to disengaged position, mechanism responsive to an exterior condition for moving said arm, a magnet exerting a force tending to hold said arm in contacts engaged position, the position of said arm with respect to said magnet being limited by the engagement of said contacts, a resilient mounting for said stationary contact, a cam surface for positively backing said stationary contact,means for moving said cam surface to vary the position of said stationary contact and the space between said arm and magnet in the contacts engaged position, and means for adjustably limiting the movement of said cam surface in its space increasing direction to set the minimum differential otainable.

14. In an electric switch, stationary and movable contacts, a switching member movable to move said movable contact to engaged and disengaged positions, mechanism responsive to an exterior condition for moving said member and means responsive to the current through the switch for moving said member to contacts disengaged position, said means constituting a unit assembly readily detachable from the switching unit without disturbing its normal operating mechanism.

15. In an electric switch, stationary and movable contacts, a switching member movable to move said movable contact to engaged and disengaged positions, opposed resilient and pressure responsive means for moving said member, a magnet biasing said member toward contacts engaged position to provide contact make and break with a snap action, and means responsive to the current through the switch for moving said member to contacts disengaged position, said means constituting a unit assembly readily detachable from the switching unit without dis-.- turbing its normal operating mechanism.

i6. In an electric switch, stationary and movable contacts, a switching member movable to move said movable contact to engaged and disengaged positions, a spring biasing said member toward contacts engaged position, a magnet biasing said member into contacts engaged position, opposed resilient and pressure responsive means for moving said member to contacts disengaged position, and a unit assembly readily attachable to and detachable from said switching unit without disturbing its normal operating mechanism and including current responsive means for moving said member to contacts disengaged position in response to an overload current through the switch.

17. Iri an electric switch, stationary and movable contacts, a switching member movable to move said movable contact to engaged and disengaged positions, mechanism responsive to an exterior condition for moving said member, means responsive to the current through the switch for moving said member to contacts disengaged position, manual means for moving said member to contacts disengaged position and for resetting said current responsive means, said means constituting a unit assembly readily attachable and detachable from the switching unit without disturbing its normal operating mechamsm.

18. In an electric switch, a switching member, separable contacts controlled by said member, mechanism responsive to an exterior condition for normally automatically moving said member, 'a unit assembly overload relay detachably associated with said. switch and having a striker biased to move said member to contacts separated position and current responsive latching means holding said striker -against said bias.

19. In an electric switch, a switching member, separable contacts controlled by said member, mechanism responsive to an exterior condition for normally automatically moving said member, a unit assembly overload relay detachably associated vwith said switch and having a striker biased to move said member to contacts separated position and current responsive latching means holding said striker against said bias, a second striker manually operable to engage-said member, and means connected with said second striker for moving said rst striker into latched position after release.

20. In a unit assembly overload relay for an automatically operated switch, a base, a rectilinearly movable striker on said base, a spring biasing said striker, current responsive latching means for said striker, a pivoted, manually operable striker, and an element rigid with said pivoted striker for engaging and moving said iirst striker into latching position after release, the pivoted striker being in operating position when resetting said rst striker.

2l. In a unit assembly overload relay for an automatically operated switch, a base, a rectilinearly movable striker on said base, a spring biasing said striker, a solder pot latching Wheel on said base for holding said striker against said bias, a series connected heater for said solder pot, a pivoted manually operable striker', and an element rigid with said pivoted striker for engaging and moving said first striker into latching position after release.

22. In a unit assembly overload relay for an automatically operated switch, a base, a rectilinearly movable strikeron said base, a spring biasing said striker, a solder pot latching wheel on said base for holding said striker against said bias, a series connected heater for said solder pot, a pivoted manually operable striker, and an element rigid with said pivoted striker for en gaging and moving said rst striker into latching position after release, and an over-center spring connected with said pivoted striker for causing its non-latching movements to be snap-like in action.

23. In an electric switch, a` switching member, separable contacts controlled by said member, means responsive to an exterior condition for normally moving said member to contacts engaged and separated positions, means responsive to an overload current condition for moving said member to contacts separated position, manual means for moving said member to contacts separated position, and means responsive to a predetermined maximum exterior condition for moving said member to contacts separated position.

24. In an electric switch, a 'switching member, separable contacts controlled by said member, pressure responsive means for normally moving said member to contacts engaged and separated positions, means responsive to an overload current condition for moving said member to contacts separated position, manual means for movlil ing said member to contacts separated position.,Y

and means responsive to a predetermined maximum pressure for moving said member to contacts separated position,v operation of each of said last three means predominating over any tendency for said first mentioned means to move the member to contacts engaged position.

25. In an electric switch, a switching member, separable contacts controlled by said member, a spring biasing said member to contacts engaged position, opposed resilient and .pressure responsive means for moving said member to contacts disengaged position, current responsive means for moving said member to contacts disengaged position, manual means for moving said member to contacts disengaged position andmeans responsive to a predetermined maximum pressure for moving said member to contacts disengaged position,'said spring moving said member to engage the contacts only when all four of said means are in inoperative position.

26. In an electric switch, a switching member, separable contacts controlled by said member, means responsive to an exterior condition for normally moving Said member to contacts engaged and separated positions, manual means for.

moving said member to contacts separated position, and means responsive to a predetermined maximum pressure condition for moving said member to contacts separated position.

27. In an electric switch, aJ switching memberF separable contacts controlled by said memben means responsive to an exterior condition for normally moving said member to contacts enmomes@ gaged and separated positions, current responsive means for moving said member to contacts. separated position, and means responsive to a predetermined maximum exterior condition for moving' said member to contacts separated position. 5

CARL A, SCI-IAEFER. 

